Telephone-exchange system



J. W. GOODERHAM TELEPHONE zxcrmmz SYSTEM Sept. 2 .1924; 1 1,507,113

Filnd Oct. 16. 192G 3 Sheets-Sheet 1 /hvenfor: v John M Goody/1am.

Sept. 2, 1924. "1,507,113

J. W. GOODERHAM TELEPHONE EXCHANGE SYSTEM Filed 0C2. 16. 1920 3Sheets-Sheet 2 Q N j S lnvenfor Jo/m W fiooo e rham.

). vMy

Sept. 2. 1-924. 1,507,113

' J. W. GOODERHAM TELEPHONE EXCHANGE SYSTEM Filed 00%.. 16. 1920 sSheets-Shea; 5

lm/enfor JO/lh W Gooderham.

Patented Sept. 2, 1924.

' UNITED STATES PATENT oF-F cr...

JOHN w. GOODERI-IAM, on NEW YORK, N. Y. assrenoaro wns rnnn nnnc'rnrocola- PANY, rnoonrona'rnn. on -NEW YORK. N. Y., A. oonPoaarlon on newYQB-K.

TELEPHONE-EXCHANGE SYSTEM;

To all whom it may concern:

Be it known that I, JOHN W. GOODERl-IAM, a citizen of the United States,residing at New York, in the county of New York and State of New York,have invented certain new and useful Improvements in Telephone- ExchangeSystems, of which the following is a full, clear, concise, and exactdescription.

change system in which connections are established through the medium ofmechanical switching devices, and more particularly to meanswhereby. asubscriber in an exchange of this character may establish a connectionto a toll olperators position for the purpose of obtaining a connectionwith a'subscribers line in a distant exchange.

In exchanges in which connections in the.

local area are established by mechanical switching devices without theservices of a central office operator, it is necessary to make provisionfor the establishment of toll connections to distant exchanges. This isordinarily accomplished. by providing a special operators position inthe full mechanical exchange with which subscribers may become connectedby dialing a signal digit 0. The operator'upon' ascertaining the connection desired, then proceeds to extend the connection to a toll operatorsposition through which the connection is further extended to the distantexchange and thence to the desired subscribers line. ing office islocated in an exchange having I a plurality of ofiices, a great savingof appa-v ratus and the employment of a less number of operators isrequired if the toll operators position is made common to all of theoffices of the exchange. To accomplish this result, however, it isnecessary to extend trunks from the special operators position of all ofthe offices of the exchange to the toll switching center, and as inlarge communities, as for example, in New York city, many of the oflicesmaybe situated long distances from said switching center. it isnecessary to provide efficient trunk lines over which full supervisionin both directions may be U0 effected.

It is therefore an objec-t of this invention to provide a toll trunk forextending a connection from a special operators position to a tolloperators position in a toll switch- Uri-- ing centerwhich affords anefficient talking This invention relates to a telephone ex When theoriginat- Application filed October 16, 1920. Serial No. 417,421.

path, and permits full supervision in bothy directions. A'furtheriobjectof the invention is to provide a toll trunk which is soarranged as to beheld busy, at its outgoing end to prevent seizure byother special .op--

erators until-after it has been freed for use atits incoming end. "A,still' further object. of-the. invention is to provide means for enabling positive supervision over the toll trunk under. all conditions ofdifferences of ground potential prevailing at the respective endsof thetrunk. A further object is to prevent differences in ground potentialfrom lmpr'operly affecting-apparatus connected to r a line at separatedpoints.

.Theseand other objects of the inventionwill be more readily understoodby reference to-the accompanying drawings in which F1gs.'1,'2 and 3taken together with Fig.

2 placed at the right of Fig. 1 and Fig. 3

placed at the right. of Fig. 2, show so much of a telephone system as isnecessary for an. understanding of the invention 102 by means, of whichacalling subscriber may extend a connection to a jackat aspccial'operators position; Fig. 2 shows so much of the circuits of thespecial operatore sion of the invention; and Fig. B'Sl'IOWS a tolltrunkcomprising the novel feature-of this invention a toll operators cordcircuit for connection with the distant incoming end of the trunkline, atoll line extending Fig. 1.. shows a calling subscribers line i A and aline switch individual to the subscribers i line, a selector switch 101and a trunk circuit to a distantexchange and the substation "circuits ofa subscribers line B terminating in said distantexchange.

It Wlll be assumed for convenience in disclosingthe invention that thesubscribefls der issued-November 1, 192-1, that the called subscribersline l3 terminates inan office Z of a distant exchange and that a tollconnection is to be established between theoi'fices X andZ through thetoll switching center Yof the same exchange asofi ice X. y

In general, the system functions .in

following manner: The subscriber 'A de-- siring a connection Withtheline of subscriber Bxin thejdistant office Z,;j removes his receiver.from; ,-its switchhook; and, throughthe operation of theiline switch 100becomes connected to a trunk line terminate...

mgin a districtselector 101. The subscriber then proceeds, to dial digitO, and, through patent, obtains a connection witha trunk circuit 102extending to a special operators position. (Fig. 2). The specialoperator:

upon answering the call ascert-ains the num ber and exchange designationof the desiredline andproceeds to set up upon (the keyboard of thesender associated with. her posi tion'such a routing as will set thedistrict selector switch 222 :upon vthe terminals of distant exchange inwhich the connection is further extended to the'line vof the desiredsubscriber B. s

As the method of extending a connection to thespecial operators-positionshown in Fig. 2 forms noessentialtpart of this invention, the apparatusfor ef'fecting such connectionhas been shown only diagram-i matically bya schematic representation of the trunk circuits and of the brushes ofthe switches 100 and 101, it beingunderstood that this' connection may,be 'madein any well-knownmanner, as for example, as dis-.

closed in the aforementioned patent.-.-

The district selector shown at 222 in Fig;

2 is of the general :type disclosed in the patent to Craft and Reynoldsh o. 1,123',696'= issued January 5, 1915*. For controlling the r acircuit is established for the line relay extending" from. groundedbat-terpcircuits associated with this selectorlswitch, an auxiliaryswitch 200 015 the= sequence switch typesu'chas disclosed in the patent.to Reynolds and Baldwin 1%, 1,1275808yissued February 9, 1915, isemployed. This auxiliary switch comprises a switch: shaft.

carrying a plurality of contact operating cams 201 to 221 inclusive,which in difler= ent angular positions effect the closure of the severalcircuits of the selector switch. Ca1n201 is a master cam andopens thecontact associated therewith only in the ositions indicated by thenumerals applied a'd-.

jacent thereto. The remaining cams close their respective contactsonlyrin the '-pos1- tions indicated by the numerals applied ad-.

jacent thereto.

The'dist 'i t selector switch 222 is selecrepresented therelays andcircuits with in the dotted rectangle marked;i Sender f?- ShQWlI he loer"leit ltand cornerrei 2. -This.-sender-.;-is of the well-known typeand since it enters only incidentally into the disclosure of thisinvention and forms no cuit byaneansof a sender selector of the wellknown type, which selector has been represented iby=the apparatusenclosed in the dotted rectangle marked Sender selec- The apparatusdisclosed in Fig. 3 for extending a toll connection from theeincomingend of the toll trunk; at office Y, to theline The 7 of aidesiredsubscriber B in ofiice'Z, has been represented .in aidiagrammaticmannersince K .the specific means for extendingsuch av con anidle trunkline extending to a tollaoper ator s position 1 in the toll switchingcenterv Y. The toll operator in 'responseto the trunksignal denoting anincoming call, 2 answers by means of her toll cord andthen proceeds inthe well-knownmanner to :e-x-i tend the connectionovera toll lin'etothe? nection is well known in the art and is immaterial to anunderstanding Of invenm,

tion having now been described, a detaileddescription of the method. ofextendinga 1 Thecalling subscriber, upon removing his receiver from theswitch hook. closes a circuitfor starting the lineiswitch. 100' in its\hunting movement in search of an idle trunk C1I0L11textending to adistrict selector-101.

As soon as an idle district selector lOl has been se1zed,.acentraloflice sender-is associ-- the district selector in the mannerfully set; forth in the application hereinbefore men- 'tioned. Thesubscriber then proceeds to dial thedigit 0 for adjusting .thewcentraloffice sender to set the district selector upon .ated with the trunkcircuit-terminating in connection, frorn-the line'of subscriber A to thehim of subscrlber B will now be given;

.a trunk circuitv 102 extending to a special operators position inthe'oifice X.

As soon as the trunkcircuit 102-is seizedo through the rightehandwinding of this re:

lay, the inner right-hand armature and-.back :1 Lcontact of cut-offrelay lOythe tip con-- "ductorot trunk circuit 102, the winding-of .al

supervisory relay ,(not shown.) associated the ring conductor of trunkcircuit 102,. the

hand winding of relay 103;. Relay 103.: 611 a closes a circuit-extendingfromjgrounded connects a. busy ground potential to the-test;

terminal 107, and .the imultiples thereof lapsr pearing-.-in the banksofall selectorshaving -i @accessato the-:trunk circuit; 1102 Thiscircuit-dfi with; district selector 101. andback through-ti 'ergizes inthis circuit a-ndat its left-hand armature andfront contact closesacircuit for the trunksignal-lamp 105;. At its right--3- hand armatureand front contact, relay 103 battery through the winding of SIOW-t'Q'IQrs lease relay 106,which relay upon. energizing tions until the specialoperator takes down the connection. 1

The operator upon noting the illumination of the trunk lamp 105, insertsthe plug 'P of an idle cord circuit of her position in the jack Jcorresponding to the trunk circuit 102 with which the trunk lamp 105 isassociated. A circuit is now established from grounded battery throughthe winding of sleeve relay 223, over sleeve conductor 224, sleevecontact 109 of plug P, sleeve contact 110 of jack J and thence tocgroundthrough the winding of cut-ofi' relay 104. Both relays 223 and 104energize in this circuit, relay 104 opening the circuit previouslytraced extending throughthe windings of relay 103, and at its outerrighthand armature and front contact closing a new circuit formaintaining the relay 106 energized. Relay 106, being slow to release,does not deenergize during the interval in which relay 103 isdeenergized before relay 104 has fully attracted its armatures. Sleeverelay 223 of the operators cord circuit upon energizing, closes acircuit for the listening-in relay 225, which circuit may be traced fromgrounded battery through the normally closed contacts of thelisteningout key LO, winding of relay 225, the lower armature and frontcontact of relay 223 and thence to ground through the upper contact ofsequence switch cam 202 (1 to 1%). Relay 225, upon energizing closes alocking circuit for itself independent of the contact of sequence switchcam 202, extending from grounded battery, through the contacts oflistening-out key LO, winding of relay 225,

left-hand armature and front contact of this relay, and thence to groundthrough the winding of relay 226. Relay 226 does not, however, energizein this circuit at this time since itswinding is shunted by a directconnection to ground through the lower armature and front contact ofsleeve relay 223, and the upper contact of sequence switch cam 202, 'butwill energize, however, as soon as the sequence switch leaves position1% as will be explained hereinafter.

Upon the energization of relay 225, energizing circuits for relays 227,228 ad 229 are established, extending from ground through the right-handarmature and front contact of relay 225, thence in parallel through thewindings of relays 227 and 228 to grounded battery and through therighthand winding of relay'229 to grounded battery. Relay 228, uponenergizing, closes a circuit extending from grounded battery through thesupervisory lamp 230,- the lower left-hand contact of sequence switchcam hereinafter. closesa locking circuit for itselfextending 203 (1 to 2and thence to ground through the armature and front contact of relay228. Relay 227 at its left-hand armature and front contact establishes acircuit for the supervisory lamp 231 extending from grounded batterythrough the lamp, the lower right-hand contact of sequence switch cam204, and thence to ground through the left-hand armature and frontcontact of re lay 227. Both supervisory lamps 230 and 231 being nowilluminated, the operator is apprised of the fact that the connectionhas beenproperly extended to the calling subscribers line and that thecircuits of the district selector 222 in which her cord circuitterminates are proceeding to function in.

the proper manner. Relay 227, at its righthand armature and frontcontact prepares a circuit for the flashing relay 232, which circuitbecomes effective later in the progress of the connection and will bedescribed Relay 229. upon energizing,

from grounded battery through the answering supervisory lamp 233, thearmature and front contact of answering supervisory relay 234, whichrelay became energized over the trunk circuit extending to the callingsubscribers line as soon as the connection was established with the operators cord circuit, thence to ground through the left-hand armatureand front contact and left-hand winding of relay At its right-handarmatureand front contact,,relay 229 closes a circuit for driving thesequence switch of the district selector 222 out of its normal position1 into position 2, this circuit extending from grounded battery throughthe driving magnet of the sequence switch 200, the upper left-handcontact of sequence switch cam 205, and thence to ground at the righ'thand armature and front contact of; relay 229. As soon as the sequenceswitch leaves posit-ion 1 the sequence switch cam 202 opens its uppercontact thereby removing the shunt from around the relay 226, and thisrelay then energizes in series with listening-in relay 225 and at itsarmatures connects the strands of the cord circuit with the operatorsset which is indicated at O. T. The operator is now enabled to conversewith the calling subscriber and receives from him instruc; tions as tothe further extension of the connection.

As soon as the sequence switch 200 reaches position 2,.a; senderselector switch. diagrammatically represented in thedotted rectanglemarked Sender selector, is started to associate a sending mechanism withthe district selector 222. Following the association of a sendingmechanism with the district-selector, the sequence switch, not shown.

but associated with the sender selector ad vances into position .4, anda circuit is there with the sending mechanism, for controlling thesending mechanism to set the brushes of the district selector 222 upon atrunk circuit extending to a toll switching center Y, and through theoperation of the routing keys, the sequence switch (not shown) butassociated with-the sending mechanism is driven out of its normalposition into posi-' tion 2,

With the sequence switch of the sending mechanism in position 2, and thesequence switch of the district selector 222 in position 3, afundamental circuit is established extending from the line relay 236 ofthe district selector, through the windings of the stepping relay 237ofthe sending mechanism, which maybe traced as follows: from groundedbattery, through the lefthand winding of line relay 236, the lowerleft-hand contact of sequence switch cam 206, the upper left-handcontact of sequence switch cam 207, the outer right-hand armature andback contact of relay 238, through the windings of stepping relay 237 ofthe sending mechanism, the armature and back contact of relay 239, andthence to ground through the contact of sequence switch cam 240 of thesequence switch of the sending mechanism. Relays 236 and 237 bothenergize in this circuit, relay 236 closing a circuit for driving thesequence switch 200 out of position 3 and into position 4:. This circuitmay be traced from grounded battery, the winding of the driving magnetof sequence switch 200, the left-hand contacts of sequence switch cam20S, and thence to ground through the righthand armature and frontcontact of relay 236. As soon asthe sequence switch leaves pOsitiOn 3,the initial energizing circuit of relay 236 is opened at the lowerleft-hand contact of sequence switch cam 206 but the line relay remainslocked up to the fundamental circuit, through its left-hand winding, itsinner left hand armature and front contact and thence to the fundamentalcircuit, through front' contact is without effect at thisztime'."

At the sending mechanism, the energization of the stepping relay 237functions in the usual manner..

When the sequence switch 200 reaches position; 4:, a c1rcu1t isestablished for the updrive magnet 211 of the district selector 222 fordriving the shaft 242 of the selector upwardly in its brush selectionmovement through the operation of updrive roller 274.. This circuit maybe traced from. grounded batter through the winding of the upedrivemagnet 241, the upper right-hand and lower left-hand contacts ofsequence switch cam V 208, and thence to ground at the right-handarmature and front contact of relay 236. During the upward movement ofthe switch shaft, a direct connectionto ground in shunt of the windingof the stepping relay 237 of the sending mechanism, is intermittentlyestablished over the following circuit: from ground, through/the lowerleft-hand contact of sequence switch cam 202- (9 to 7), shaft wiper 243,the brush selection segment 24% of the commutator 24:5 and thence to ajunction point in the fundamental circuit-be tween the windings ofrelays 236 and 237 at the lower right-hand contact of sequence switchcam 206 closed in position 3% to 4 Upon each connection of the shunt.circuit, as previously traced, the stepping relay 237 of the sendingmechanism deenergizes to operate the counting relays of the sending backcontact opens the fundamental circuit, previously traced, through thewindings of relays 236 and 237. Upon the opening of the fundamentalcircuit, relay 236 deenergizes, opening at its. right-hand armature andfront contact the circuit previously traced extending through thewinding of the up-drive magnet 241, thereby causing the switch shaft tobe arrested in its upward movement with a certain one-of its brush setspositioned in such a manner with respect to the tripping spindle 21 26as to cause such set of brushes to be tripped when the tripping magnet247 is later energized and the switch shaft is again driven upwardly. Atits right-hand armature and back contact, relay 236 closes a circuit foradvancing the sequence switch 200 out of position 4 and into position 5,this circuit extending from grounded battery through the winding of thedriving magnet of the sequence switch 200, the lower contact of sequenceswitch cam 209 and thence-to ground at the back contact andright-handarmature of relay'236f A circuit is now- Co-unting established for thetrip magnet 247, extending from grounded battery through the winding oftrip magnet 247, and thence to ground through the right-hand contact ofsequence switch cam 210.

lVith the sequence switch of the sending mechanism in position 4, andthe sequence switch 200 in position 5, the fundamental circuit extendingthrough the windings of relays 236 and 237, is again established andthese relays both energize as previously described. Relay 236, uponenergizing, closes a circuit extending from grounded battery,

through the winding of the driving magnet of sequence switch 200, theleft-hand contacts of sequence switch cam 208, and thence to ground atthe right-hand armature and front contact 236, for driving sequenceswitch 200 out of position 5 and into position 6. Upon leaving position5, the initial energizing circuit of relay 236 extending over thefundamental circuit, is opened at the lower left-hand contact ofsequence switch cam 206, but the relay is maintained energized over itsleft-hand winding, its inner left-hand armature and front contact andthrough the upper left-hand contact of sequence switch cam 206 andthence over the fundamental circuit. With the sequence switch inposition 6, the circuit of the updrive magnet 241 is again establishedover the circuit previously traced, and the switch shaft is now drivenupwardly in its group selection movement by the updrive roller 274.During this upward movement of the switch shaft, a ground is connectedintermittently to the fundamental circuit between the windings of relays236 and 237 over a circuit which may be traced from ground at the lowerleft-hand contact of sequence switch cam 202, shaft wiper 276, the groupselection segment 248 of commutator. 245, and thence to the fundamentalcircuit through the upper right-hand contact of sequence switch cam 206(5 to 6). In response to the upward movement of the switch shaft, thestepping relay 237 of the sender is intermittently operated in thewelllniown manner until the counting relays of the sending mechanismhave counted down in accordance with their setting as determined by therouting registered by the operator. When the counting relay energizes,-the sequence switch of the sending mechanism is advanced from position'4 into position 6 in the well-lmown manner, and relay 239 whichenergizes in parallel with the O counting relay, opens the fundamentalcircuit at its armature and back contact.

In response to the opening of the fundamental circuit, relay 236deenergizes, opening at its right-hand armature and front contact, thecircuit previously traced extending through the winding of up-drlvemagnet 241 to arrest the tripped set of brushes of the selector switchon the lowermost set of terminals of the selected group of bank.terminals. At its right-hand armature and back contact, relay 236 closesthe circuit previously traced for driving the sequence switch 200 outofposition 6 and into position 7. Upon reaching position 7, a circuit isestablished for the relay 236 which may be traced from grounded batterythrough the righthand winding of relay 236, and thence to ground throughthe lower contacts of sequence'switch cam 211. Relay 236, energizing inthis circuit closes a circ'uit for driving the sequence switch 200 outof position 7 into position 8, this circuit extending from groundedbattery through the driving magnet of sequence switch 200, the left-handcontacts of sequence switch cam 208 and thence to ground at'the armatureof relay 236. As soon as the sequence switch leaves position 7the'energizing circuit of relayv 236 is opened at the lower right-handcon-.

tact of sequence switch cam 211. Relay 236 however, remains energizedover a locking circuit extendlng through its left-hand winding, itsinner left-hand armature and front contact, the upper contacts ofsequence switch cam 212, the outer left-hand armature and front contactof relay236, the up per right-hand contact of sequence switch cam 221,test brush 249 andthence to the lowermost test terminal 250 of the groupof trunk lines to which the selected brush set has been moved if thefirst trunk line of the 1 group is busy. If this first trunk line,however, is at the time idle, the'locking circuit for relay 236 is notestablished and relay 236 immediately deenergizes thereby preventing theestablishment of a circuit for the updrive magnet 241 and the operationof the 3 switch in its trunk hunting movement when the sequence switchreaches position 8.

Assuming, however, that the first trunk line of the group is busy, relay236, remains locked up after the sequence switch leaves position 7 and acircuit is thereupon estab lished for-the up-drive magnet 241, whichcircuit may be traced from grounded bat 'tery, through the winding ofmagnet 241, the upper right-hand and lower left-hand contacts ofsequence switch cam 208, and

ing from grounded battery, through its right-hand winding, the lowerleft-hand and .nals of the selected idle trunk, since relay 236 is heldenergized overa circuit extend upper right-hand contacts of sequenceswitch cam 211, the centering segment 252 of the commutator 2&5, switchshaft wiper 253, the lower contacts of sequence switch cam 208 andthence to ground at the armature and front contact of relay 236. Thiscentering locking circuit is opened as soon as the wiper engages aninsulating portion of segment 252 corresponding to the positionof-switch shaft 242 in which the brush set is properly centered on theselected set of trunk terminals.

Relay 236, upon deenergizing in addition to opening the circuit ofup-drive magnet 2&1, closes a circuit extending from grounded battery,through the winding of the driving magnet of sequence switch'200, thelower left-hand contact of sequence switch cam 209 and thence to ground,through the righthand armature and back contact of relay 236, fordriving the sequence switch out of .position 8 and into position 9.Relay 236 now closes a circuit for placing ground potential upon thetestbrush 249 of the selector switch to mark the selected trunk circuitas busy to other selector Switches which have access thereto, thiscircuit extending from ground, through the upper left-hand contact ofsequence switch cam 210 (7 to 9) the inner left-hand armature and backcontact of relay 236, the left-hand contacts of sequence switch cam 212,overflow segment an of commutator shaft wiper 255 and thence to testbrush 249. The selected trunk circuit is also held busy by groundpotential connected to the test and over the circuit previously traced,this ground potential being maintained. on the test brush 249 throughposition 11 of 1the.

sequence switch.

During the setting of the selector switch 222, supervisory lamp 230 wasmaintained illuminated over a circuit extending from grounded battery,through lamp 230,the upper lett hand contact of sequence switch cam 203and thence to ground at the left-hand armature and back contact of relay256. Lamp 231 was maintained illuminated over a circuit extending fromgrounded battery, through lamp 231 and thence to ground through thelower left-hand contact of sequence switch cam 204, the illumination ofthese lamps signifying to the operator that selection is proceeding.

As soon as the sequence switch 200 reaches position 9 since, at thistime, the sequence switch of the sender selector is in position 8following the registration of the routing of the connection upon thesending mechanism,

a circuit is established for advancing the sequence switch 200 out ofposition 9 and into position 10, this circuit extending from groundedbattery, the windingof the driving magnet of sequence switch 200, thecontacts of sequence switch cam 213 (9), contact of sequence switchcam257 of the sequence switch (not shown) of the sender selector, andthence to ground at sequence switch cam 2&0 of the sequence switchassociated with the sending mechanism. Ifthe trunk circuit which hasbeen selected is inproper condition for extending the connection, se-

quence-switch of the sending mechanism is now advanced in the well-knownmanner intoposition 7, and a circuit is then closed for'advancing thesequence switch 200 into position 11, this circuit extending fromgrounded battery, through the winding of the driving magnet of sequenceswitch 200, the lower right-hand contact of sequence switch cam 205, andthence to ground at the left-hand contact of sequence switch cam 258."As soon as the sequenceswitch 200 leaves position 10 the circuit ofsupervisory lamp 231 is opened at sequence switch cam 204-, and sincenow lamp 230 is illuminated and lamp 231 is dark, the operator isapprised of the fact that selection has been completed.

lVhen the sequence switch reaches position 11, a fundamentalcircuit isestablished extending-through the windings of relays 236 and 237 whichmay be traced from grounded battery, through the left-hand winding ofrelay 236, the lower left-hand contact of sequence switch cam 206, theupper left-hand contact of sequence switch cam 207, theouterright-handarniature and backicontact of relay 238, windings ofrelay 237,, armature and back contact of relay 239 and thence to groundthroughthe contacts of sequence switch cam v259. Relay 236, energizingin this circuit, closes at its -right,-hand armature. and front contact,

a circuit extending through the left-hand contacts of sequence switchcam 208 for drivingthe sequence switch 200 out'of position 11.-Rela'y236 is maintainedenergized after the sequence switch leavesposition ll. and opens the lower left-hand contacts of sequence switchcam 206, over a circuit extending through its left-hand winding, its

inner left-hand armature and front contact and-thence through the upperleft-hand contact of sequence switch .cam 206 and over the fundamentalcircuit as previously traced.

The sequence switch in passing position 11% establishes a directconnection to ground between -the windings of relays 236 and 237, thiscircuit extending from ground, through the lower contact of sequenceswitch cam 20'? and thence to the fundamental circuit at the upperleft-hand contact of sequence switch cam 206. In response to theconnection of direct ground to the fundamental circuit, the steppingrelay237 of the. sending mechanism. deenergizes, and in the well-knownmanner controls the energization of one of .the'counting relaysassociated with the send ing mechanism. As the sequence switch 200passes positions 12 13 and 14%, v the stepping relay 2370f the sendingmechanism 5 is further intermittently deenergized and if in the caseassumed, the sending mechanism has been so adjustedby the depression ofthe routing keys as to cause the 0' counting relay to be energized onlywhent-he sequence switch 200 has passed position 14%, then gized inparallel with relay 0, opens thev 'iundamental circuit thereby causingrelay to become deenergized to open the driv- -1ng circuit of thesequence switch 200 to arrest the sequence switch in position 15,

The advance of the sequence switch 200 under the control of the sendingmechanism,

is for the purpose of connecting the sec- -ondarywindings of repeatingcoil 260 with the brushes of the selector switch in different ways inaccordance with the class of connection being-established, for affordingthe most efiicient talking path. For this purpose the right-handwindings of the repeating coil 260 may-be divided into sections andplaced under the control of the district sequence swit'cln'as fullydisclosed in the aforesaid patent issuedito F. A. Stearn and F. J.Scudder.

lVith the sequence switch of the cord circuit in position-15, a circuitis established for the flashing relay 282, which may be traced fromgrounded battery through the winding of relay 232, the right-handarmature and front contact of relay 227, and

thence to ground through the upper lefthand and also right-hand contactsof sequence switch cam 221. Relay 232, upon energizing, opens at thenormal contactsof its armatures, a direct connection between theright-hand windings of the repeating coil 260 and the'contacts ofcams214 and 53 215, and interpo-ses in this connection the normallyclosed contacts of the operators flashing key 277. After leavingposition 11, the circuit previously traced extending from the left-handarmature and back contact of relay 238 to the brush 249 for holding theselected toll trunk busy, is opened at the lower right-hand contact ofsequence switch earn 212 and the selected trunk circuit isthen held busythrough position of the '63 sequence switch over a circuit extending igrounded battery through the winding of from brush 249 through shaftwiper 255, overflow segment 254 and to ground through the'upperleft-hand and lower right hand contacts of sequence switch cam 211,

In position 15 of the sequence switch,

quence switch earn 214-, the upper armature circuit is establishedforthe line relay 300 associated with the outgoing end of the selectedtoll trunk circuit which may be traced from grounded battery through theright hand winding of relay 300, the innermost upper armature and backcontact of switching relay 301,"the tip conductor 302 of the selectedtrunk circuit, bank terminal 261 .and brush 262 of selector 222, thecontact of seand front contact of flashing relay 232,the normally closedright hand contacts of flashing key 277, the upper make contactsassociated withthe upper armature of relay 232, the upperright-handwinding of repeating coil 260, the contact of sequence switch cam 216(14% to 15), the winding of polarized supervisory relay 263 the contactof sequence switch cam 217, the lower right hand windlng of repeatingcoil 260, the make contacts. associated with the lower armature of relay232, the-normally closed left-hand contacts of flashing key 277, thelower ari'nature and .front contact of relay 232, contact of se q uenceswitch cam 215, brush 264 of selector 222, terminal 265, ring conductor303 of the selected tolltrunk circuit, the lowerinnermost armature andback contact of switching relayBOl and thence to ground through theleft-hand winding of relay 300. Relay:- 263 closes a circuit which maybe traced from grounded battery, through the winding of relay 256, righthand armature and back contact of relay 266 and thence to ground throughthe armature and front contact of relay 263. Relay 256, upon energizingcloses a locking circuit for itself extendingthrough its winding, itsinner right hand armature and front contact and thence to ground,through the lower right hand contact of sequence switch cam 202 (2 to18),

At its lefthand armature and front contact,

' relay 256 establishes a new circuit for lamp 230 which may be' tracedfrom grounded battery through the lamp, the'upper right hand contactofsequence switch cam 203, the left-hand armature and back contact ofrelay 266 and thence to ground through-the left hand armature andfrontcontact of relay 256, thus placing the lamp 230 under the 1joint'control of relays256 and 266. At its outer armature and-frontcontact,-relay 256 completes a circuit for relay 266 which cir,

.cuit becomes effective as soon as supervisory relay 263 deenergizesupon the response of the toll operator at the switching center Y. Relay300 associated with the incoming end of the toll trunk uponenergizing,establishes 'a circuit for sleeve relay 30d of the tolltrunkywhich circuit may be tracedfrom relay 304-, the armature and frontcontact of relay 300, sleeve conductor 305, bank terminal25l and test,brush 2&9 of selector switcli222,-;and thence over'the circuitpreviously hand contact' of sequence SWltClL'CaIn- 211. Relay 304, uponenergizlng 1n thls' circuit,

traced toground atthe lower-right ground ithrough the winding of relay3l6. Re'lay 316', upon"energizingg'closes a circuit for -the trunk lamp-318 associated With-the closes a circuit extending from groundedjack Jin'W-hicli the selected toll tr-uninterbattery, tl'irough the Winding ofsloW-to-re-- n' 'inates. lease relay 306*a'nd to ground at the left'Tlie'toll operator zit-position O in-the 'toll hand armature and frontcontact' of relay.-'switchingcenter Y, in'- "responSe to the'il- 304. Atits-right-hand armature and outer lurn ination of .the- *trunk lamp 318inserts front contact, relay 1 establishes a lockthe plug P o-fone ofthe *tolhcordc'ircirits ing circuit for itselfe-xtend-ing directly'to'at her -position in the jack J of the toll the sleeve conductor 305independent of the "trunk with'Whichathe;illuminatedlamp318 arniaturesof line relay300,and at 'itsrig'htis associated,- Whereupon a ci rcuitisrestabhand arn'iature and inner front-contact es lished which may betraced from grounded tablishes a circuit for switching relay 301,battery through the winding: of theemarwhich may be traced from groundedbat- =-gina:1' sleeve relay-319 of the cord-circuit, tery through thewinding of this relay through tl1'G"Sl8VeOOIltL0t 320 of theplug throughthe right hand armature and inner P, the sleeve contact321ofthe jack Jand "rent contact of relay 30 i and thence to 'thencetoground througli-'the left -"hand ground over the sleeve conductor'305fl Re- Winding of;cut oif relay 1315. Cut-offrelay lay 301 energizing in this circuit.disconnects 315 "energizes lIff-thlS'. cr-rcuityopening' at' its thewindings of line relay 300 from the tip left-hand armaturecontacts-thecircuit preand ring conductors 302 and 303 ot-the viously t-racedextendingthrough the-windtrunk circuit, and connectsthese' conductorsxings'of'relay 31 1*, and at its left-hand armato the conductors 307 and308 respectively tures and front 'contactsrconnects the flashof theoutgoing end of the trunk circuit ex ing supervisory relay 322 with thecontending to the distant toll switching center. ductor's 307 and 308-of the tolltrunk.- At

' At its outermost armatures aiicl-backcontactsitsright-handarni'at'ure' -and frontcont'act,

be described hereinafter.

relay 301 disconnects the conductors 309 and relay 315establishes acircuit for 'the-slow- 310, which conductors are normallyconnectto-release relay 317 which; upon" energizing,

ed to the trunk conductors"307 i1 and '308 opens the circuit of'relay-316 to extinrespectively. *"Q'LilSll' the lamp 318. At "itsarmature-and SloW-to-release relay 306, uponenergizing, frontcontactyre-lay 317 establishes adocking establishes a circuit for relay311', Which circircuit for itself extending to the armature cuit may betraced fronr grounded battery antl iront contact of "relay 314iWhich-locking throughthe winding ofrelay 311 and the" circuit becomes"efi ective-toi hold -the relay rigl1t-lia-nd arniature of relay 306 andrelay 317 energized at a later stage in the estab- 311 uponenergizing,connects the windings llSllHlBIlfiOf the connection. o'l'relay 312 and of differential relay 313 to Due to-tlressubstitutionofthe direct bridge the conductors 309'and 310 for a-purpose tor acrossthe conductors 308 and 307' ofthe trunk line,* through-theWinding-ofrelay As soon as relay 301 has oined the t1p -32Qin placeof.bnidgedbattery at the Windand ring conductors of the incomingandvingsof'relay'31t, th -p l iz d i outgoing ends of-the toll trunk, acircuit is "r l yn263 at the ial t d i established for the line relay31:4'ass0ci-ated zcuit in Fig. 2, is-deprived of its energizing with thedistant end'of the trunk circuitwcurrent' andthereupondeener'gizes,=closing The circuit of this relay may be tracedfront atits armature and back contact a circuit grounded battery,through the right hand for relay-266,- extending fromgrounded-batwindingof relay 314, the innerlefthand i't ry th hith -i -i di fyelay Q66 tharmature and baclccontact of cut-off relay l r it ts f it h glg 315,conductor 308, the innermost lowerwthe 'outerrightvhand armature andfront armature and front contact of switching contact of relay 256-, andthence-toground relay 301, CODdUCtOl' 303, {t'IlCl thence 0V6]? the 5 atth'e: amnaturenandback ontact of relay circuit previously traced,through the W'i-DCl- 263.=---'Relay 266, upon energizing;opensthe ing ofrelay 263, and back over trunk c0n circuitofsupervisory lamp 230 at" itsleft ductor 302, the innermost upper armature handarmature andbackcontact and since, and front contact'oi relay 301, conductor" at thi'stime, supervisory-lamp 231 is" ex- 30T,-the outer left hand armature andback -tinguished; the special operator iS' given a contact of relay 315and thence to'grounch'signa-lthat a connection has been establishedthrough the left hand "Winding of relay 31 1. with thetolhswitclringcenter anc'lthat the Relay311'i, energizing in this circuit, 8St&b":tblloperator 'has responded.,- At -itsleft lishes a circuit for'thelaniprelay 316 Which hand armature and front oontact,:relay266 circuitextends vfrom grounded battery establishes a locking circuit-foritselfexthrough the armature and front contact-ct tendin'gto ground attheleft hand armature relay 314, the armature andiback contact-of andfront-contact of relay 256 and-prepares sl0W-torelease' relay 317 andthence to a-circuit for supervisory lainp 231 which circuit becomesetlectiveup'onthe subsequent energization of polarized supervisory relay263' when the distant toll operator disconnects from the toll trunkeither tor. the purpose o't flashing the special operator or for givingthe special opera-tor a disconnect signal. z

At the. toll switching center, marginal relay 319 does not energize andtherefore no circuit is closed for the supervisory lamp The tolloperator after establishing a connection with the toll trunk, throwsherlistening key 32 1 to connect her headset with the cord circuit whichshe has employed and over the connection established with the specialoperator (Fig. 2) obtainsrinstruc tions for further extendingthe-connection. It having been assumed that a connection is desired withthe subscribers line B which tern'iinates in an office Z of a distantexchange, the toll operator will obtain the assignment of .a trunkcircuitextending to the desired exchange and will then insert the plug Pof the cord circuit in the jack J of the assigned trunk, whereupon acircuit will be 1 established from ground through the sleeve contacts ofthe plug and jack, winding of relay;325, resistance 326, and thence togrounded battery. The energization of relay 325 joins the tip of theplug P with the tip strand of the operators cord circuit. r s

Following the extinguishing .-ofsupervisory lamp 230 denoting that thedistant toll operator hasv answered the call, the special operator maylisten out on the connec- .nection by depressing the listeningoi'it'keyLO opening the locking circuit of listeningin relay 225 whichdeenergizes and opens the circuits of relays 227,228 and 229. Relays227, 228 and 229 deenergize when the locking circuitof relay 225 isopened. Relay 226 which is also energized in this looking circuit alsodeenergizes disconnecting the operators set fromtheanswering end'ot thecord circuit and connecting the answering end of the cord circuitdirectly to the lefthand windings of the repeating coil 260. It theoperator wishes to listen in again ona connection, she depresseslistening-in key LI which closes a. circuit extending from groundedbattery, through the normally closed contact of listening-out hey LO,the winding-of relay 225, the lower. armature and trout contact of relaycontacts of listening-in key L1 to ground at the lower contact of thesequence switch cam202. lie-- lay energizes in this circuit .closing alocking circuit for itself extending through its left hand armature andfront contact and to ground as previously described, through the windingof relay 226, relay 226 thereupon reconnects the operators headset tothe cord circuit.

If the operator wishes to flash thetoll operator in the distant tollswitcl1ing.cen.- ter, she throws the flashing key 277 =toc0nnectgrounded battery and ground to. the

tip and ring strands of the out-going end" of her cord circuit foroperating .therelay 322 at the distant end of the toll trunlr307 and308. ;The energizing eircuitofrelay 322 may be traced from groundedbattery,

through resistance element 268, through the 3 right hand contact of key277, theJupper, armature and front contact of flashingrelay 232,:contact of sequence iswitchcam21a, Y

selector switch brush 262, bank terminal 261,

trunk conductor 302, the innermost upper armature of swltching relay 301and its front contact, trunk conductor 307, theouter lefthand armatureand front contact of.

relay 315, the winding of flashing supervisory relay 322, the innerletthand arrnature and front contact of relay 315, trunk conductor-308,the innermost lower armature and 'trontco ntact of relay 301, itrunlrcon ductor303, bank terminal 265,:switch'brush 264., contact ofsequence switch cain215, lower armature and front contact/of flash ingrelay 232, the left-hand contact of l iey 277 and thence to groundthrough the resistance element 269. Relay 322, in response to eachoperation of the, flashingkey 277, attracts its armature therebyconnectingthe right hand winding. of relay 315. in parallel with theleft hand winding of thisu'elay thereby reducingthe resistance of thesleeve trunk circuit and connects the windings of relay 01 i and bridgedbat-teryto the conductors of the trunk. -::In response tothe connectionof bridged battery across the conductors ot the trunk circuit,.thepolarized supervisory relay 263 at the specialopei atorscord;circuitbecomes energized to close a circuit extending from:grounded battery,

through the super'visory'lamp 231, armature and front contactoi'relay-266 and to ground 1 atthe armature and front contactot'relayv263. Thusin responseto each withdrawal of the plug P from the jack J,the-lamp 231, at the specialoperators cord circuit,

flashes to signal.

give the special operator a recall Followingthe extension of theconnection to the trunk line terminating at the toll operators positionin jack J and extending to the distant exchange, the connection isextended in the well-known manner at such distant exchange to the officeZ in which the desired'line B terminates and the subscriber on line B iscalled in the usual manner.

Upon the termination of the conversation between the subscriber A inoflice X and the subscriber B in office Z, the calling subscriberrestores his receiver to its switchhook thereby opening the circuitpreviously traced extending through the supervisory relay 234. Thisrelay thereupon deenergizes, opening the locking circuit previouslytraced, through the left hand winding of relay 229, and connects thesupervisory lamp 233 in a circuit extending from grounded batterythrough the lamp 233, the armature and back contact of relay 234 andthence to ground through the lower contacts of sequence switch cam 210.The operator, noting the illumination of lamp 233, then proceeds to takedown the connection by withdrawing plug P from the jack .1. lVhen theplug is withdrawn from the jack, the circuit existing through thewindings of cut-off relay 104 of the trunk 102 and the sleeve relay 223of the cord circuit, is opened and the relays deenergize. Since, at thistime, relay 229 is deenergized, a circuit is established for relay 238which may be traced from grounded battery, through the winding of relay238, the left hand contact of sequence switch cam 219, the upperarmature and back contact of sleeve relay 223 and the right handarmature and back contact of relay 229 to ground. Relay 238, energizesin this circuit and at its inner right hand armature and front contact,closes a locking circuit for itself extending to ground at the lowerright hand contact of sequence switch cam 202. At its left hand armatureand front contact, relay 238 closes a circuit for driving the sequenceswitch 200 out of the talking position 15 and into position 17, thiscircuit maybe traced from grounded battery through the winding of thedriving magnet of sequence switch 200, the lower right hand contact ofsequence switch earn 220 and thence to ground at the left hand armatureand front contact of relay 238. Upon reaching position 17, a circuit isestablished for advancing the'sequence switch into position 18, whichcircuit may be traced from grounded battery, through the winding of thedriving magnet ofsequence switch 200, the upper right hand contact ofsequence switch cam 219, the upper armature and back contact of sleeverelay 223 and thence to ground at the right hand armature and backcontact of relay 229.

With the sequence switch in position 18, a

circuit is established for the down-drive magnet 2700f the selectorswitch 222, which circult' may be traced from grounded battery throughthe winding of magnet 270 and thence to ground through the upper contacts of sequence switch cam 220. The'en' ergization of down-drivemagnet 270 in the a well-known manner through theope'ration of thedown-drive roller 275 drives the switch shaft 242 downwardly into'its no1' mal position. When the switch shaft reaches its normal position, acircult is es-f tabhshed for driving the sequence switch out of position18 and into its-normal posi- At the trunk circuit 102 upon thedeenergization of relay 104, the circuit of relay 106 is opened at theouter right hand arma' ture and front contact of relay 104,- and sinceat this time thereis no energizing circuit for line relay 103, thecalling subscriber having restored his receiver to the switch hook,relay 106 disconnects ground poiten tial from the test terminal 10?causing there by the release" of selector switch 101, and of line switch100. All the apparatus in the originating oflice X is now innormalposition.

Upon the restoration of the district selector switch 222, the sleevecircuit over which relay 304 ofthe toll trunk was held energized isopened at sequence switch cam 211 and this relay deener'gizes thereby0pm ing the circuit of switching relay 301, which upon deenergizingopens the tausn onductors of the trunk circuit and at its outermostarmatures connects the windings of relays 312 and 313 to the conductors307 front contact of relay 312 and thenceto ground through thearmatureand front con} tact of relay 306. Relay 306 is thus main tainedenergized after theinitial energizing circuit is opened upon thedeenergization of sleeve relay 304 to maintain relay 311 611;

ergized and busy ground potential connected to conductor 305 until thedistanttoll operator disconnects. The energization of of supervisoryrelay 319, and these relays deenergize, relay 319 extinguishing thesignal lamp 323, and relay 315 disconnecting the Winding of relay 322from the conductors of the trunk circuit and connecting the windings ofrelay 314 in place thereof. The circuit through the'right hand windingof 1 relay 314 may nowbe traced from grounded battery, the right handwinding of this relay, the inner left hand armature and back contact ofrelay 315, conductor 308, the lowermost armature and back contact ofrelay 301, conductor 309, the inner left hand armature' and frontcontact of relay'311, the left hand winding of relay 312, the leftjhandwinding of differential relay 313 and thence to grounded battery. Thecircuit through the left hand winding of relay 314 may be traced fromground throughthe left hand winding of this relay, the left hand arma,ture and back contact of relay315, conductor 307, the uppermost armatureand back con- 3 tact of relay 301, conductor 3.10, the outer right hand.armature and front contact of relay 311 and to groundthrough ,therighthand windings of relays 312 and 313. It is to. be noted that thebatteries atthe respective ends of the trunk circuit are now con nectedin opposition and therefore relay 312 associated with the outgoing endofthe trunk circuit becomes. currentless and. y deen'ergizes, opening atlts armature and front 1 contact the locking circuit previously tracedthrough the relay 306 which relay thereupon decnergizes opening thecircuit of relay 311.

r The trunkcircuit is now restored to normal position.

The relay 312 is so wound as to release upon eight volts difference ofpotentialbetween batteries at the respective ends o f the toll trunk.If, however, there is a substantial difference in ground. potentialbetween the oppositeendsof the trunk circuit, relay preventing theseizure of the trunk circuit 312 may fail to release when the tolloperator disconnects from the distant end of the toll trunk, andtherefore relay 311may be maintained energized to maintain a busy groundpotential'on thexmultipletestterrninals of the trunk circuit appearingin the banks of. districtselectors in the office X,

for a new connection even after the trunkcircuit has been freed for use.at bdth of its' ends. To ob-viate'such a false condition,

differential relay is proi idedjwhich re n lay will not operate undero-rdina'ryHcondi tions, but will operate if there is such a dif ferenceof ground potential between the respectiveends of the trunk circuit aswill prevent the release of relay 312. 'lNhen relay 313 energizes undersuch conditions, upon the disconnection of the toll operators cordcircuit from the distant end of the toll trunk,

the holding circuit of relay 306 isopened at thereby permitting therelease of, relay 3:11

and the disconnection of busy potential from the sleeve conductor 305 ofthe tollt runki If the toll operator at the toll'switch-ing center, isthe first to disconnect from thetoll' trunk, the release oftheconnectionproceeds' in the following 'manner& Upon the with d-rawal ofplug P from the jack J, relay.

315 deenergizes thereby connecting the windings of relay 314 to theconductors 307 and 3080f the tolltrunk and since, at this time,thefspecial operatorhas not pulled down the connectionat her positionand the switching relay301 is energized over a circuit extend ing overthe sleeve conductor 305, they relay 314is therefore connected in a!circuit inseries with the supervisory relay 263: at the the armature andback contact of .relay313,- 5

special operators position. Thesuperv'isory' relay 263 energizes n thiscircuitandclose's a circuit for the supervisory lamp 231, which may, betraced from grounded battery through lamp 231, the right hand armatureand front contact of relay 266 and thencev to ground throughthe armatureand front contact to relay 263.

supervisory lamp 233 is illuminated in-the manner previously described,and the operator noting the illumination of the: supervisory, lamps 231and 23.3, proceedsto withdraw the plug P from the jack J, and theapparatus in the office X which' was employed'in the establishment ofthe con'nec tion, is restored in the manner previously described. Whenthe selector switch222 re-v When the subscriber restores l'llS receiverto' its switchhook, the;

stores and moves its brushes from the ter-" I minals of the selectedtrunk 'cir'cuit,'th e cir cuit of sleeve relay 304 ofthe toll trunkis.opened, and this relay becomes deenergized opening the circuit ofswitching relay 3 01 and the circuit'o-f relay'306. gUponthedeenergization of switching relay 301 andlthef connection ofthewindings of relays312: and i 313 to the conduetor 307 and "308 ofthtrunk cir'cuit,i,.the.relays" 312 and not 1 I energize since'atthistirn'ethe operator at the 2 tollswitching. center has :disconnec tedandthere is nov direct. bridge across the'incofn ing endof the trunkcircuit for providinglan.

operating, circuit. for] relays 312.;

Z Therefore, there is, at this time 'no'holdin'g circuit for relay306aiid' this relaydeeneh gizes openingthe circuit of relay 8l1whicjh inturn' removes busy potential from the sleeve conductor 305 of theti'unlicircuit.

If the calling subscriber abandons the call prior to the establishmentof a? toll connection with the selected toll tr inlr, that is, when thesequence switch200 is iii' positions 2'to 9, the apparatus isi'estoredin the following manner: upon restoratioii of subscribers receiver tothe switchhook,

supervisory relay 234 becomes deen'ergizedi thereby opening the lockingcircuit of relay 229', and closing a circuit fo'i" illuminatingsupervisory lamp 233i 111' responseto the lamp signal, the operatorwithdraws plug P from jack J thereby opening the'circuit of sleeve relay223; A" circuit is niow closed for relay 238 which may be traced fr'omgrounded battery throi'igh the winding of relay 238, the upper left handcontact of sequence switch cam 2 19 (2 to9), the up per armature andback Contact of relay 22 3,,

and thence to ground at the right hand armature and back contact of;reia 'eea Relay 238, upon energizing, locks up to ground at cam 202,opens the fundamental circuit atits outer right hand arinature and backcontact, and at its left hand armature and front contact closes a'circuit for driy ing the sequence switch 200 into position 10. Thiscircuit may be traced from grounded battery, through the wiiiding oftion, a circuit is closed for driving the sequence switch 200 out ofposition 10 and into normal position this circuit extending fromgrounded battery, through ,the wind ing of the driving nagnet ofsequence switch 200, the upper right hand contact of sequence switch cam205, normal com inutatorsegment 271, shaft wipe'r2i 6 and thence to aground: through the, lower, left hand contact of sequenceswitch cam 202.

' Should a, selector'switch fail to find an idle trunk circuit in theselected" group during its trunk hunting movement I when the sequenceswitch associated therew th is in. position 8, a flashing signal" willbe given to the special operator in the following manner: as soon as theset of tripped brushes mote upwardly beyond the set ofterminals in theselected group, the line relay 236 which was locked up so long as testbrush'2'd9 encountered terminals of busy trunks, dee'nergizes, and atits right hand armature and back contact, closes-a circuit for drivingthe sequence switch out of posij tion 8 and into posit on 9, thiscircuitex'tend' ing from. grounded: battery, through the winding of themagnet of Sequeiice Switch 200 the lower. left hand contactof sequenceswitch cam 209 and'therioe to ground at the right hand armatureand backcon tact of relay 236. Upon reaching position 9, the sequence switch isadvanced in the manner hei'einbefhre' described, by the send? er intoposition 10, Since now the shaft wiper 243 is standing upon theconducting portion ofthe commutator 272, a circuit is nowestablished'for driving the sequence switch into position 11, thiscircuit maybe traced from grounded battery, through the winding of thedriving v niagnet of sequence switch 200, the lower lefthandfcontaot ofsequence switch cam 205, segment,27 2, brush 2&3 and thence to groundthrough the lowerleft handcontact of se'q ueii'ce"switch cam 202. Inposition 11, a circuit isestablished fi'oni'ground on the egimn'rme asprevious ly traced, through'the'lower contacts of sequence switch cain206 and thence through the left hand winding of relay 236 to groundedBattery. Relay 236 energizes in,

this circuit and closes locking circuit for itself extending from:grounded battery through its left hand winding, its inner left handarmature and frontcontac't, the left hand and lower right liandconta'ctsof sequence switch cam 206' a nd thence to ground through segmenti272'as previously traced. Relay 236 remains energized throughposition 1 5the sequenceswitch" and closes at its right hand manu land front contacta circuitjfor driving the se-l quence switch into'p'osition 16. Thisciifcuit may be traced from grounded battery;

through the winding of the driving magnet of sequence switch 200, theleft handicontacts of sequence switch c'ain 208and thence to ground atthe right hand armature and front contact of relay 236' hen the sequenceswitch reaches position 16, a circuit is closed for flashing thesupervisory lamp 231, which may be traced from grounded battery, throughthe lamp 231, the upper contacts of sequence switch cain 218* and thenceto ground through the interrupf The operatoig in respons'e tfo theflashing signal, may then lis'ten in'on the connec-; tion in the mannerpreviously descrihed v and inform the calling subscriber thattlie'i'e'ar e no idle toll trunks available for use at that time. Theconnectionmay then be restored in the manner previously described.

While in the foregoing description, the special toll trunk shown in Fig.3 has been described as employed in connection with a selector switch atthe special operators' position for seizing its out-going end, it willbe apparent to those skilled in the art that the trunk circuit mightreadily be adapted to be employed in a manual exchange and seized at itsoutgoing end by manual means What is claimed is: c 1. In a telephoneexchange system, an originating oflice, a distant oi'iice, a trunk lineextending between said offices, means at said first office for seizingsaid trunk line, means at said second office for extending a connectionfrom said trunk line, a relay at the outgoing end of said trunk lineresponsive to the seizure theerof, means controlled by said relay andeffective upon the release of said trunk line at its outgoing end, forrendering said trunk line busy at its out-' going end, and meanscontrolled over said trunk line and effective upon the seizure of saidtrunk line and the subsequent release thereof, for maintaining saidrelay energized until connection with 'said'f trunk line has beendisestablished at said distant office.

2. In a telephone exchange system, an originating oflice, a distantoffice, a trunk line comprising two conductors only extending betweensaid ofli'ces', means at said first ofiice forseizing said trunk line,means at said second office for extending a connection from said trunkline, a relay at the outgoing end of said-trunk line responsive to theseizure thereof, means controlled by said relay and effective upon therelease of said trunk line at its outgoing. end for rendering said trunkline busy at its outgoing end, and means controlled over the conductorsofsaid trunk line in series and effective upon the seizure of said trunkline'and the subsequent release thereof for maintaining said relayenergized until connection with said trunk line has been disestablishedat said distant oflice. I v a 3. In: a telephone exchange system, anoriginating office, a distant office, a trunk line comprising twoconductors only extending between said offices, means at said firstoffice for seizing said trunk line, means at said second office forextendinga connection from said trunk line, a relay at theout going endof said trunk line responsive to the seizure thereof, means controlledby said relay and effective upon the relcase of said trunk line at itsoutgoingend for rendering said trunk line busy at its outgoing end, anda double wound relay controllable over the conductors of said trunk linein series'and energized upon the seizure of said trunk line and thesubsequent release thereof for maintaming said first-namedrelayenergized,

until connection with saidtrunk line has been disestablished atsaiddistant office.

4. Ina telephone exchange system, an

originating ofiice, afdistant office, a trunk line comprising twoconductors only, ex-

tending between said ofiices', means at saidfirst office for seiz ngsaidotrunk hne, means at said second oflice for'extendin'g a connectionfrom said trunk line, 'a relay at the outgoing end of said trunklineresponsive to the seizure thereof, means controlled by said relayand efiective uponthe release of said trunk line at its outgoing end forre dermg said trunk line busy at its outgoing mg the release of saidfirst-named; relay upon failure of said secondmamed relay'to release thefirst-named relay upon the disestablishment of the connection atvsaiddis tant oflice.

5. In a telephone exchange system, an I originating office, a distantoffice, a trunk line extending between said offices, means at said firstoflice forlseizing said trunk line, means at said second office forextending a connection from said trunk line, a relay at the outgoing.end of said trunkline responsive to the seizure thereof,means-controlledby said relay and effective, upon the release of'the outgoing end ofsaid trunk line for renderingsaid trunk linebusy at its outgoing end,means controlled over said trunk line and effective upon the seizure andthe subsequent release of said trunk line for establishing a holdingcircuit for said relay until connection with said trunk line is disestablished at said second office, and a differential relay operableoyer said trunk line fOropening said holding circuit upon re lease ofsaid trunk line at said second o-ffice when the difference of groundpotential between said oflices is sufiicient to prevent the release ofsaidlast namd means. i i

6. In a telephone exchange system, any: originating office, a distanto'fiice,fa trunkv line extending between said offices, means at saidfirst office for seizing said trunk line, means at said, second office'for extending a connection from said trunk line, a relay at the outgoingend of said trunk line respon-' sive to the seizure thereof, meanscontrolled by said relay and effective upon the release of the outgoingend of said trunk line for rendering said trunk line busy at. itsoutgoing end, a double wound relay. and a diflerential relay associatedwith the outgoing end of said trunk line, and means effective latterrelays with said trunk line whereby said double wound relay is energizedover said trunk line to establish a holding circuit for said first-namedrelay until said trunk line is released at said second office andwhereby said ditij'erential relay is energized over said trunklinelollowing the release oi said trunk line at said second otfice toopen said holding circuit when the dili'erence of ground potentialbetween said ofiices is sutficient to prevent the release of said doublewound relay.

'2". In a telephone exchange system, an originating otlice, a distantoliice, a trunk line extending between said oliices, means at said firstotlice for seizing said trunk line, means at said second o'tfice forextending a connection from said trunk line, a relay and a source ofcurrent associated with each end of said trunk line. and meansassociatedwith each end of said trunk line and effective uponthe releaseof the respectiveends of said trunk line it'orbridgingthe respectiverelays and sources of current across said trunk line whereby whensaidtrunk line is free at each o't its ends, said relays are connectedin opposition oversaid trunk line.

8. In a telephone exchange system, an originating otfice, a distantotfice, a trunk line. extendingdretween saidotfices, a relay and asource of current at each. oliice adapted to be connected in bridge withthe. respective ends of said trunkline in such a manner as to be inopposition when both of said relays are connected to said trunk line,and a differential relay associated with one end of said trunk line andadapted to be operated over said trunk line when a dilierence ofgroundpotential exists betweenthe respective ends ofsaid trunk line.

:9. in a telephone exchange system,v an originating oflice, a distantoffice, .a trunk line extending between said ottices, means at saidfirstofiice vfor seizing said trunk line, a cord circuit at saidsecondo'tfice for extending a connection from said trunkli'ne, a linerelay normally bridged across said trunk line at said second olfice, acutoff re.- lay ,energized upon connection with said trunk line fordisconnecting said line relay from said trunk line, a flashing relayadapted to be bridged across said trunkline upon the encrgizationotsaidcutofi relay, a flashing, key at said'first oflice forintermittentlyrenergizing said tlashingrelay, and a supervisory signalassociated with said cord circuit and under the control of said flashingrelay.

10. In a telephone exchange system, an originating otfice, a distantoiiice, a trunk line extending between said offices, means at said'firstoflice for seizing said trunk line, a cord circuit at said second ofiicefor extending a connection from said trunk line, a line relay normallybridged across said trunk line at said second ofiice, a cutofi relayenergized over the sleeve conductor of said cord circuit upon connectionwith said trunk line for disconnecting said line relay from said trunkline, a flashing relay adapted to be bridgedacross said trunk line uponthe energization of said cutoff relay, a flash-e ing key at said firstotiice tor intermittently energizing said flashing relay, a supervisorysignal associated with said cord circuit, and means controlled by saidflashingrelay' for increasing the flow or, Current in said sleeveconductor to operatesaid signal.

11. The combination of'a telephone line, supervisory apparatus connectedtheretoat separated points and subject to diiierence of groundpotentials, with compensating means operative over said line andresponsive t said difference of potential for preventing said difierence of potential from improperly affecting said apparatus. k

12. The combination ot a telephone line, and supervisory apparatusconnected thereto at separated points and subject to difference ofground potentials, with automatic controlling means for said apparatusoperative over said line and responsive to said difierence of potential.v

13. In a telephone exchange system a first operators position, a secondoperators position, a trunk circuit extending between said positions, asignal atthe second 0pera'tors position, a link circuit at the'first anda link circuit at the second operators position, a supervisory signaltor each of said link circuits,,means responsive to the connection ofthe link circuit at said first position with saidtrunk circuit foractuatsaid first signal, means responsiveto the connection of the linkcircuit at said second position with said trunk .circuit forextinguishing said signal and means responsive tovthe disconnectionotjthe link circuit at said first position for operatingthe supervisorysignal of said link circuit at said second position and for renderingsaid trunk circuit busy until the link circuit at said second positionis disconnected. I

In witness whereof, I hereunto subscribe name this lth day OfrOCtOlJQl,A.,D 1920. 1 v i JOHNWV; GOODERHAM.

